In the production of aluminium with an electrolytic furnace it is desirable to preclude the so-called anode effect by injecting a gas, usually air, into the molten aluminium. To achieve this it is known to break up the crust which forms on the top of the molten aluminium and then to use manually-operated probes or lances to blow air into the molten aluminium thus exposed. From German patent specification No. 1608232 it is known also to constructionally unite the lances with the crust-breaking tools in an apparatus mounted over the bath containing the molten aluminium. The present invention relates to an apparatus of this type and has as its object the provision of improvements to the apparatus.